The present invention relates generally to dynamometer and power absorption devices and, particularly, to an improved dynamometer capable of more accurate power measurements and which is easily adjusted, serviced and maintained.
Several different types of dynamometers have been developed in the past. Basically, these prior art devices fall into three broad categories: mechanical brakes which depend upon frictional energy conversion, hydraulic brakes which absorb mechanical energy by shearing a working fluid, and electrical brakes which utilize variations in field forces or reversals in electric polarity as a means of energy conversion.
Examples of typical prior art mechanical and hydraulic dynamometers are illustrated in U.S. Pat. Nos. 3,068,689 and 3,757,909. While such dynamometers have been generally adequate in the past, several particular problems and disadvantages have become apparent.
Dynamometers of the type disclosed in the first of the above-mentioned patents have proven inadequate at higher RPMs. The mechanical braking mechanisms tend to "fade" or wear excessively at such higher speeds which results in inaccurate measurements. Moreover cavitation may be a problem because, as the coolant surrounding the rotating drum begins to rotate with the drum, centrifugal force causes a void along the surface of the drum. This greatly diminishes the cooling capability of the dynamometer. Maintenance presents obvious difficulties in such prior art devices since the entire dynamometer is enclosed in a water-filled housing. Finally, the cooling water in which the rotating drum is immersed causes a drag on the rotation of the central elements of the machine. Since this drag is often not capable of measurement in conventional apparatus, the accuracy of the dynamometer is adversely affected.
Hydraulic dynamometers such as that disclosed in the latter of the above-mentioned patents are often of much simpler design than mechanical apparatus. However, cavitation is also a problem which not only results in excessive wear but also adversely affects the accuracy of such apparatus. Furthermore, hydraulic dynamometers of the prior art often rely on the accurate flow control of working fluid, normally water, which is introduced at various rates into the apparatus to measure the power of the prime mover. An apparatus of this type often does not provide the accuracy of mechanical dynamometers where such flow is constant and generally not critical for the proper measurement of power.